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GCSE Biology Summary Notes The Nervous System
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Summary Notes on the GCSE Biology topic The Nervous System, specifically curated for the AQA Biology Exam Board.
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The Nervous SystemNervous System
The nervous system enables humans to react to their surroundings
and coordinate their behaviour.
Cranial nerves go from your brain to your eyes, mouth, ears and
other parts of your head.
Central nerves are in your brain and spinal cords.
Peripheral nerves go from your spinal cords to your arms, hands, legs
and feet.
Autonomic nerves go from your spinal cords to your lungs, head,
stomach, intestines, bladder and sex organs.
Receptors
These are cells that can detect a stimulus. A stimulus is anything in the environment that
triggers a nerve impulse. They are:
Eyes (rod and cone cells) – light and colour rod and cone
Tongue – chemicals cells
Skin – change in temperature, pressure and pain
Nose – chemicals
Ears – sound and balance
Sensory Neurone
These carry electrical impulses from a receptor to the central nervous system. These are
long, thin and highly branched.
Central Nervous System
These are made up of the brain and spinal cord. It acts as a coordinator and sends a
response. The relay neurons carry messages from one part of the CNS to another.
Motor Neurone
Carries impulses from the central nervous
system to an effector. There are some
adaptations:
, Highly branched dendrites that can make connections.
Thin
Long axons carry impulses
Insulating sheath
Carry electrical impulses very fast, 120m/s.
Lots of mitochondria provides energy needed to make transmitter chemicals.
Nerve ending pass impulses between cells.
Effector
A muscle/ gland that produces a response, e.g. a muscle contracting to move an arm, a
muscle squeezing saliva from salivary glands and a gland releasing hormones into the blood.
Examples of Reflex Arc
Stimulus Light in eye Bee stings Standing on Dust Change in
hand Pin Temperature
Receptor Rod and Pain Pain Eye Change in
cone cells in receptors on receptors temperature
eye Skin on Skin receptors on skin
CNS Brain Spinal Cord Brain Spinal Cord Brain and Spinal
Cord
Effector Muscles in Muscles in Muscles in Muscles in Sweat glands
eye contract arm contract leg contract eyelid contract release sweat
Response Pupil Arm moves Leg moves Blink Sweat
constricts away
Reflexes are important as they keep you from harm, as they
are automatic, involuntary, rapid actions.
The brain may not be involved with a reflex if the spinal cord
is closer so the reflex is quicker. The electrical impulse travels
to the nearest place to speed up the response. The brain is
informed later so you can act in a sensible way according to
your injury e.g. plaster.
Synapses
There are synapses between a sensory neurone and a relay neurone
in the CNS, a chemical (neurotransmitter) is released that causes an
impulse to be sent along a relay neurone. A chemical is then
released in the synapse between a relay neurone and a motor
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